1. Field of the Invention
The present invention relates to the stacking of sheets, e.g. printed sheets. In particular, the present invention relates to a sheet stacking device and a method of stacking sheets.
2. Background of the Invention
In conventional sheet stacking devices, for example, sheets are deposited consecutively onto a sheet receiving plane, thereby forming a stack of deposited sheets. Depositing a sheet may comprise inverting the sheet around an axis of rotation.
From EP 1 762 523 A2, a sheet stacking device is known that comprises a rotatably arranged element for inverting and conveying a sheet onto a receiving plane. At least a portion of a sheet to be stacked is accepted in a slot at the circumferential edge of the rotatably arranged element, and is rotated until it reaches the stop and emerges from the slot while the rotatably arranged element rotates further. In order to restrict the freedom of movement of the edge of any sheets that have already been deposited on the receiving plane, retention hooks are provided for exerting a downwards directed retention force onto the sheet edge.
FR 2 760 733 A1 discloses a similar sheet stacking device with flexible support elements 47a, 47b and fingers 46 for pressing on the upper sheet of the stack.
From DE 199 57 574 A1, an apparatus and method for depositing sheets on a stack are known. Tongues, a hold-down, and rollers are used for pressing on a top sheet of a stack. While the tongues and the hold-down are positioned on top of the stack, a new sheet is advanced onto the stack by the rotation of the rollers. While the sheet is held by the rollers against the tongues, the hold-down is lifted and placed onto the new sheet on top of the stack. Afterwards, the rollers and the tongues are lifted off the stack, and the tongues are placed on top of the stack, again.